Problem with GPIO3_18

Gilberto Ermacovitch

We have developed a custom board based on the AM335X processor. We use the GPIO 3_18 to control a RS484 transceiver. However, we experiencing problems (the pin is always in logical 0) in trying to toggle a GPIO 3_18 using the sysfs interface described in the following link: www.kernel.org/.../sysfs.txt .
I am wondering if there is some restrictions in using the GPIO3_18 has an output.
Please advice.
BR
Gilberto

over 10 years ago

0 guillaume piot over 10 years ago

Prodigy 40 points

There is no restriction using GPIO3_18 as an output.

Try this in order to configure gpio3_18 as an output (high level)
echo 114 > /sys/class/gpio/export
echo high > /sys/class/gpio/gpio114/direction

If the output remains low, maybe you have to check the pin multiplexing.

0 Gilberto Ermacovitch over 10 years ago in reply to guillaume piot

Prodigy 210 points

Hi

The GPIO 3_18 is still in low logic level. Furthermore, I believe the GPIO 3_18 is configured as an INPUT (or in high impedance at least).
The mapping I am using in the board.c file is:

{"mcasp0_aclkr.gpio 3_18", OMAP_MUX MODE7 | AM33XX_PIN_OUTPUT},

Is there any mapping in UBOOT needed for this configuration? I believe that Linux can overwrite any previous UBOOT mapping.

Thanks in advance,

Gilbertio

0 guillaume piot over 10 years ago in reply to Gilberto Ermacovitch

Prodigy 40 points

Do you use the device tree functionnality ? uboot can load a dtb file at startup. Verify the uEnv.txt file

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Problem with GPIO3_18